Q-factor and waveguide-sphere separation effects in waveguide-coupled microsphere resonators

Quality-factors of waveguide coupled microsphere resonators of 30 μm diameter are measured. A Teflon buffer layer is deposited on the waveguide to separate the microsphere from the waveguide and the effect of this separation on the measured quality-factor is discussed. The whispering-gallery mode propagation along the cavity of the microsphere as well as the optical path lengths of the modes are determined; the experimental and theoretical data are compared and discussed. A five-fold increase of the Q-factor was obtained by increasing the sphere-waveguide separation.